Bellows talk: Tube vs accordion

Discussion in 'Gas Engines/Drives/Transmissions/Props' started by Nova_Gts, Jul 20, 2019.

  1. Nova_Gts

    Nova_Gts New Member

    4
    Aug 7, 2017
    1998 290 Dancer
    454 B3
    I wanted to publish a little information because I've seen a lot of debates on whether there are any differences.

    Background: I have a 98 290 with a single 454 Bravo 3, while I specifically wanted this under-powered combination, any time something isn't on point, I notice.
    I recently replaced the transom assembly (which comes from merc with the accordion), and was struggling to get on plane. After hours of diagnostics and a full tune up, I finally decided to hone in on the fact that the exhaust note had changed. After reading many opinions, mostly claiming that it is preference and noise reduction, I decided I'd gamble with the $50 part and try swapping out my bellows.

    Findings: The tube style bellows was just the boost I needed to get over the hump and on plane; I also regained about 100 rpm at WOT. However, as one would expect, its a straight win win. When I had the accordion, the acceleration from around 2500 to 3600 rpms was much faster, but the power curve would fall off right after that and not allow me to hit the 3800 I need to plane.

    Hope this information helps anyone wondering about this in the future.
     
  2. scoflaw

    scoflaw Well-Known Member

    Aug 10, 2011
    cape cod mass, cape coral fl
    1999 Powerquest legend 260 sx
    502 mpi Bravo 1
    You must of had some kind of obstruction in the leg, maybe some old shutters. Your results aren't normal.
     
  3. Nova_Gts

    Nova_Gts New Member

    4
    Aug 7, 2017
    1998 290 Dancer
    454 B3
    Interesting theory. Any more insight as to why you think it?
     
  4. scoflaw

    scoflaw Well-Known Member

    Aug 10, 2011
    cape cod mass, cape coral fl
    1999 Powerquest legend 260 sx
    502 mpi Bravo 1
    Lots of boaters do that just because the tube is easier to install. The general report back is slightly louder and no talk about performance.
     
  5. Nova_Gts

    Nova_Gts New Member

    4
    Aug 7, 2017
    1998 290 Dancer
    454 B3
    Routing the exhaust all the way through the drive and out the back increases back pressure. It's not as much of an issue on smaller blocks, but it does cause issues on the big blocks.
     
  6. scoflaw

    scoflaw Well-Known Member

    Aug 10, 2011
    cape cod mass, cape coral fl
    1999 Powerquest legend 260 sx
    502 mpi Bravo 1
    I haven't notice any improvement. Got Captains call, straight shot out the transom
     
  7. Nova_Gts

    Nova_Gts New Member

    4
    Aug 7, 2017
    1998 290 Dancer
    454 B3
    With a boat that is adequately powered you wont notice minor gains, I need every bit of power I can get so minor changes are noticable
     

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